Problem: Ishaan was assigned problems 49 through 69 for homework tonight. If Ishaan did all of the problems he was assigned, how many problems did he do?
Explanation: Instead of counting problems 49 through 69, we can subtract 48 from each number so we instead consider problems 1 through 21. We see that Ishaan did 21 problems. Notice that he did 21 and not 20 problems.